Guide wires are used to guide a catheter in treating sites at which open surgery is difficult or which require minimal invasiveness to the body, for example, PTCA (Percutaneous Transluminal Coronary Angioplasty), or in examination such as angiocardiography. A guide wire used in the PTCA procedure is inserted, with the distal end projecting from the distal end of a balloon catheter, into the vicinity of a target angiostenosis portion together with the balloon catheter, and is operated to guide the distal portion of the balloon catheter to the target angiostenosis portion.
In PTA (Percutaneous Transluminal Angioplasty) also, for opening a stenosis portion (occluded portion) in a peripheral blood vessel such as femoral, iliac, renal and shunt blood vessels, a distal portion of a balloon catheter is guided to the vicinity of an angiostenosis portion by use of a guide wire, like in the PTCA procedure.
Since the blood vessels to which such a treating method is applied are bent in a complicated manner, a guide wire used to insert a balloon catheter into the blood vessel is required to have, for example, appropriate flexibility and resilience against bending, pushability and torque transmission performance (generically called “steerability”) for transmitting an operational force from the proximal portion to the distal side, and further, kink resistance (resistance against sharp bending) and the like.
Guide wires intended to provide steerability and flexibility at the distal portion of the guide wire include guide wires formed from different materials, particularly guide wires having a first wire composed of an Ni—Ti alloy and a second wire composed of stainless steel.
In the above guide wire, the first wire composed of an Ni—Ti alloy and the second wire composed of stainless steel are joined by butt resistance welding, whereby the first and second wires can be joined comparatively firmly, as contrasted to other welding methods where a brittle Fe—Ti based intermetallic compound would be produced with the result of insufficient joint strength.
In addition, the weld portion is provided with a projected portion projected in the outer circumferential direction (radially outward direction) so that the joint strength is enhanced by the projected portion and the stress generated when the guide wire is bent is dispersed.